1. Field of the Invention
The present invention relates to tire valves, particularly to safety inflation and deflation valves and a cap for such valves.
2. Description of Prior Art
Vehicle tire manufacturers recommend that tire pressure be measured under a normal load [(i.e., a vehicle with one or two occupants) and moderate temperature, i.e., about +20.degree. C. (68.degree. F.)].
During driving, however, the tire may experience extreme conditions, such as a high ambient temperature, an increased load, and/or a long period of high-speed driving. Such extreme conditions may increase the pressure inside the tire to a value exceeding its upper allowable limit. This may cause the tire to blowout, i.e., violently rupture and tear, causing a total loss of pressure and collapse of the tire.
In the past, many types of valves have been devised to release excess pressure if it exceeds a predetermined maximum allowable level. One such device is described in U.S. patent application Ser. No. 07/481954 filed 02.20.90 by me with coinventors. This device comprises a special core for a standard tire valve. This core contains an additional safety valve adjusted under factory conditions to the maximum allowable pressure for each specific tire.
Although such a safety valve with an additional core is convenient for tires newly manufactured at automotive plants, they are inconvenient for installation on existing tires. This is because for installation of such a core into an existing tire, one has to completely deflate this tire, remove the old core, replace it with a new one, and then to inflate the tire to a pressure recommended for the tire of this type.
Another disadvantage of the safety valve with a new insert is that it is unsuitable for use with a standard cap normally threaded onto the tip of the tire valve for its protection from dirt, water, etc. This is because the standard cap would block a path for air to be released from the tire through the the safety valve proposed by the above-mentioned patent application. Therefore a nonstandard, i.e., specially designed cap is required.
As the new core, which contains a valve, has to be inserted into a small-diameter channel of an existing tire valve housing, its own channel is so small in diameter that the absolute value of air pressure developed in this channel is very low. Therefore technical problems may occur in selecting proper materials for the additional valve core. More specifically, this problem is associated with the construction of the spring which has to develop a force sufficient to deform the valve seal.
Another attempt to solve the above problem is to use special safety caps with means for generating a light signal when the pressure exceeds the maximum allowable level. Such safety tire-pressure indicating valve caps are produced commercially, e.g., by Herrington Co., Londonderry, N.H. 03053.
The main disadvantage of such safety caps is that they only give light signal indication about overinflation or underinflation of air pressure in the tire, but do not provide automatic control or adjustment of the tire pressure during driving. In order to check the pressure via a light indicating signal, the driver must stop the vehicle in a dark place, or at least in the shade, to clean the indicator head, if it is dirty, and then to adjust the pressure manually (after removing the cap), either by releasing the pressure, or by pumping additional air. In other words, this is a passive method of control. Moreover, it is inconvenient.